Available here are some links to websites useful to students, especially 4th graders.
Math
A Plus Math (matho, concentration, hidden picture)
FunBrain (variety of games)
Math Baseball
Math Magician Games (20 questions in a minute, choose mult table)
Multiplication Hidden Picture (no choice of problems)
Pick a Number

Science
EduPlace
Kelp WebCam
Great Plant Escape (great!)
Leaf Types
Parts of Flower